Current non-invasive tests to measure intestinal transit time or detect bacterial overgrowth are largely based on the use of substrates (e.g., .sup.14 C-xylose) which are either almost exclusively metabolized by bacteria or are malabsorbed and subsequently split by colonic bacteria, e.g., .sup.14 C-glycocholic acid. Isotopically labeled CO.sub.2 or unlabeled metabolites (e.g., H.sub.2) that result from the bacterial degradation of substrates of this type may then be absorbed, transported by the circulation, and finally exhaled by the lungs. Typical tests based on this concept are the .sup.13 C-urea breath test and the lactulose-hydrogen breath test. The reliability of these tests, however, may be limited by irregularities in gastric emptying, rapid absorption and renal excretion of the substrates, intestinal recycling, and intermediary metabolism. Consequently, there is a need for tracer substances which are characterized by minimal absorption and endogenous degradation, but which are acted upon by specific bacterial enzymes that bring about the release, absorption, and exhalation of labeled volatile metabolites. In addition, the extension of the benefits of breath test analysis to studies of infants and children, and women of reproductive age demands the development of nonradioactive alternatives to .sup.14 CO.sub.2 tests that are currently used.
Estimates of transit time in the gastrointestinal tract depend upon: (1) the time for initial or peak appearance of hydrogen in breath from the bacterial fermentation of a non-absorbable sugar, for example, lactulose; (2) the appearance of chromium oxide or styrofoam markers in the stool; or (3) the fluoroscopic examination of the passage of radio-opaque markers through the intestinal tract.
These measurements are inaccurate and/or burdensome. For example, breath hydrogen measurements are inaccurate and not reflective of true mouth to colon transit times. In addition, there are "non-responders" to the H.sub.2 breath test in the normal population. Ingestion of stool markers requires collection and examination of the stool and limits the number of studies that can be performed on the same individual over a short period of time. Fluoroscopic examinations present a radiation hazard. These inaccuracies and burdens are significantly reduced or absent in the procedure of the present invention. Further, the present procedure offers numerical characterization of transit processes that are independent of observer judgment.
Glycosyl ureides are condensation products of reducing sugars and urea. They were first described in 1903 and their chemical and physiological properties have since been repeatedly studied. In the glycosyl ureides, the molecular linkage between the carbohydrate and the urea has been shown to resist cleavage by gastrointestinal enzymes, but is capable of being split by colonic flora. The resistance of the glycosyl ureide bond to enzymatic cleavage was noted as early as 1931 using glucose ureide as a model. Most of the microbes tested in vitro failed to release glucose from glucose ureide. Selected putrefactive bacteria, however, were shown to decompose glucose ureide to ammonia. Further, urease from soybeans does not split glycosyl-bound urea. Nevertheless, as shown in the present invention, enzymatic cleavage of monosaccharide units from disaccharide ureides does not seem to be difficult for intestinal and bacterial enzymes. Glycosyl ureides apparently are partially absorbed but undergo no appreciable metabolism. Although many of the chemical and physiological properties of the glycosyl ureides are known, until the present invention, there has been no use of, or suggestion of use of, the glycosyl ureides (1) to measure gastrointestinal motility, (2) to monitor treatment, (3) to diagnose disease, or (4) to monitor drug transit in the gastrointestinal tract.
A primary basis for using the .sup.13 C-labeled glycosyl ureides of the present invention as markers for the bacterial colonization of the intestine is their poor absorption. High absorption rates would prevent these substrates from reaching the terminal ileum, where bacterial colonization starts in normal man, and thus no knowledge would be gained on intestinal transit time. If early bacterial degradation products are formed and absorbed, however, their excretion could indicate bacterial overgrowth.